Illumination system and method for recycling light to increase the brightness of the light source

ABSTRACT

An illumination system for increasing the brightness of a light source comprises an optical recycling device coupled to the light source, preferably light emitting diode (LED), for spatially and/or angularly recycling light. The optical recycling device spatially recycles a portion of rays of light emitted by the LED back to the light source using a reflector or mirror and/or angularly recycles high angle rays of light and transmits small angle rays of light, thereby increasing the brightness of the light source&#39;s output.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of application Ser. No. 11/818,308filed Jun. 13, 2007 now U.S. Pat. No. 7,976,204, which claims thebenefit of U.S. Provisional Application Ser. No. 60/813,186, filed Jun.13, 2006, U.S. Provisional Application Ser. No. 60/814,605, filed Jun.16, 2006, U.S. Provisional Application Ser. No. 60/830,946, filed Jul.13, 2006, U.S. Provisional Application Ser. No. 60/842,324, filed Sep.5, 2006, U.S. Provisional Application Ser. No. 60/848,429, filed Sep.28, 2006, and U.S. Provisional Application Ser. No. 60/855,330, filedOct. 30, 2006, each of which is incorporated herein by reference in itsentirety. This application is a §371 of PCT/US2006/041592 filed Oct. 25,2006, and claims priority from U.S. Provisional Patent Application No.60/730,171 filed Oct. 25, 2005.

BACKGROUND

This invention relates to systems and methods for increasing thebrightness of illumination systems, particularly for an illuminationsystem and method that recycles light emitted from a light source inorder to increase the brightness of that light source.

Light sources are used in all types of illumination applications.Typical light sources include but are not limited to arc lamps,halogens, fluorescent devices, microwave lamps, and Light EmittingDiodes (LEDs). Many applications require an illumination system with ahigh level of brightness in a small effective emitting area. This highlevel of brightness can be accomplished conventionally by adding morelight sources. However, this can be both technologically impossible ifthere is a limited space for integrating light sources and economicallyunfeasible as it can be expensive to integrate and use multiple lightsources. Accordingly, the present invention proceeds upon thedesirability of increasing the brightness of a light source withoutincreasing the number of the light source.

For example, microdisplay based television (MDTV) has the potential ofbeing low cost with large screen size. Traditional MDTVs are usuallyilluminated by arc lamps. Although this light source is the brightest atthe lowest cost, the need to split the white light into 3 colors and theshort lifetime make it less desirable. With advances in LED technology,the use of LED as the light source in MDTVs has to be considered tocapture the long life feature of LEDs and other benefits such as instantON. However, at the present time, LEDs are not bright enough for lowcost application using small imaging panels or with larger screens. LEDrecycling scheme has been used to enhance the brightness of the lightsource, see U.S. Pat. No. 6,869,206 issued to Zimmerman et al. However,Zimmerman et al. describes enclosing the LEDs in a light-reflectingcavity with one light output aperture. Also, U.S. Pat. No. 6,144,536issued to Zimmerman et al. describes a fluorescent lamp having a glassenvelope with a phosphor coating enclosing a gas filled hollow interior.A portion of the light generated by the phosphor coating is recycledback to the phosphor coating. The present invention proceeds upon thedesirability of providing a recycling device that can be coupled to oneor more LEDs to increase the useable brightness of the LED by recyclingefficiently such that smaller panels can be used or large screens can beilluminated with sufficient brightness.

For example, LEDs are one type of light source used in many illuminationapplications such as general lighting, architectural lighting, and morerecently in projection televisions. When used in projection televisionsfor example, LEDs must emit light in a small effective emitting area ata high brightness level in order to provide the requisite high lightoutput on the television screen. Specifically, the LEDs must provide anintense and bright light as measured in lumens at a small and solidangle in a small emitting area to be useful in projection televisions.Unfortunately, the currently available LEDs are not bright enough to beuseful in illuminating large projection television screens, which areincreasingly popular with the consumer.

Therefore, there is a need for a method and system for increasing thebrightness of LEDs so as to provide an illumination system that meetsthe demands of the current and future applications at a reasonable cost.

SUMMARY OF THE INVENTION

Therefore, it is an object of the present invention to provide anillumination system that solves the aforesaid problems of the prior art.

Another object of the present invention is to provide the illuminationsystem comprising a recycling device to recycle a portion of the lightemitted by the light source to increase the brightness of the lightoutput.

A further object of the present invention is to provide the illuminationsystem comprising a spatial recycling device for recycling light byreflecting a portion of the light emitted by the light source back tothe light source to increase the brightness of the light output.

A still another object of the present invention is to provide theillumination system comprising an angular recycling device fortransmitting small angle light and recycling high angle light toincrease the brightness of the light output.

A yet another object of the present invention is to provide theillumination system comprising a spatial and angular recycling devicefor recycling a portion of the light emitted by the light source toincrease the brightness of the light output.

A still yet another object of the present invention is to provide theillumination system as aforesaid, which additionally comprises apolarizer to reflect and recycle the light with undesirablepolarization, thereby enhancing the recycling effect of the recyclingdevice.

The present invention is directed to an illumination system thatrecycles light to increase the brightness of a light source, therebyenabling the illumination system to provide a higher output of light ata reasonable cost. In accordance with an exemplary embodiment of thepresent invention, the illumination system for recycling light toincrease brightness comprises a spatial recycling device. The spatialrecycling device comprises a light pipe which is coupled to the lightsource, preferably a LED chip mounted on a substrate. The spatialrecycling device recycles light by covering a portion of the output endof the light pipe with a reflective medium or coating so that the lightfrom the light source is reflected by the reflective medium back intothe light source through the light pipe. The light source re-emits thereflected light into the light pipe, thereby increasing the brightnessof the light output from the illumination system.

In accordance with an exemplary embodiment of the present invention, theillumination system for recycling light to increase brightness comprisesan angular recycling device. The angular recycling device comprises atapered light pipe coupled to a light source, preferably a LED chipmounted on a substrate. Preferably, the tapered light pipe isdecreasingly tapered light pipe where the light pipe tapers from alarger cross-sectional dimension at the input end to a smallercross-sectional dimension at the output end. The angular recyclingdevice transmits small angle light and reflects large angle light backinto the light source. The light source re-emits the reflected light ata different angular distribution, thereby increasing the brightness ofthe light output.

In accordance with an exemplary embodiment of the present invention, theangular recycling device comprises a decreasingly tapered light pipecoupled to a light source, preferably a LED chip mounted on a substrate,and an increasingly tapered light piped coupled to the output end of thedecreasingly tapered light pipe. The decreasingly tapered light pipetapers from a smaller cross-sectional dimension at the input end to alarger cross-sectional dimension at the output end. The angularrecycling device transmits small angle light and reflects large anglelight back into the light source, thereby increasing the brightness ofthe light output.

In accordance with an exemplary embodiment of the present invention, theangular recycling device comprises a lens system coupled to a lightsource, preferably a LED chip mounted on a substrate. The lens systemscomprise a lens surface or lens at the center surrounded by concavereflectors or reflective surfaces. Alternatively, the reflectors can bedual paraboloid reflectors where the high angle rays of light arereflected twice before being focused back onto the LED chip. Thereflectors and reflective surfaces reflect the high angle rays of lightback into the LED chip for recycling and the lens or lens surfacecouples the small angle rays of light as light output, therebyincreasing the brightness of the light output.

In accordance with an exemplary embodiment of the present invention, anoptical recycling device to increase the brightness of a light sourcecomprises a transmission medium for transmitting the plurality of raysof light from the light source. The transmission medium has an outputend and input end coupled to the light source. A mirror or reflector iscoupled to the output end of the transmission medium for recycling aportion of the plurality of rays of light by reflecting the portion ofthe plurality of rays of light back to the light source through theinput end of the transmission medium to be re-emitted by the lightsource, thereby increasing the brightness of the light source's output.

In accordance with an exemplary embodiment of the present invention, amethod for increasing the brightness of an illumination system comprisesthe steps of: providing a light source and a light pipe comprising aninput end and an output end; the light pipe further comprising areflective medium disposed on the output end; producing rays of light bythe light source; positioning the light pipe so that the input end issubstantially proximal to the light source; collecting rays of light atthe input end; reflecting a portion of the rays of light by thereflective medium back into the light pipe; coupling the reflected raysof light with light emitted from the light source; outputting thereflected rays of light from the output end of the light pipe, therebyrecycling light to increase the brightness of the illumination system.

In accordance with an exemplary embodiment of the present invention, amethod for increasing the brightness of an illumination systemcomprising the steps of: providing a light source and a tapered lightpipe having an input end and an output end, wherein the light pipetapers from a larger cross-sectional dimension at said input end to asmaller cross-sectional dimension at the output end; producing rays oflight by the light source; positioning the tapered light pipe so theinput end is substantially proximal to the light source; collecting therays of light at the input end; reflecting a portion of the rays havinglarge angles back into the tapered light pipe decreasing therebydecreasing the angle dimension; outputting small angle light from theoutput end.

In accordance with an exemplary embodiment of the present invention, amethod for increasing the brightness of a light source, comprises thesteps of: coupling an optical recycling device to a light source toreceive a plurality of rays of light from the light source; recycling aportion of the plurality of rays of light back to the light source; andre-emitting the portion of the plurality of rays of light to the opticalrecycling device by the light source, thereby increasing the brightnessof the light source's output.

Various other objects, advantages and features of the present inventionwill become readily apparent from the ensuing detailed description, andthe novel features will be particularly pointed out in the appendedclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description, given by way of example, and notintended to limit the present invention solely thereto, will best beunderstood in conjunction with the accompanying drawings in which likecomponents or features in the various figures are represented by likereference numbers:

FIG. 1 is a cross-sectional side view of an LED chip mounted on asubstrate;

FIG. 2 shows the LED of FIG. 1 coupled to a light pipe;

FIG. 3 is a cross-sectional view of an illumination system in accordancewith an exemplary embodiment of the present invention, showing areflector or mirror covering a portion of the output end of the lightpipe;

FIG. 4 shows the illumination system of FIG. 3 additionally comprising apolarizer covering a portion of the output end of the light pipe notcovered by the reflector in accordance with an exemplary embodiment ofthe present invention;

FIG. 5 is a cross-sectional side view of an illumination system inaccordance with an exemplary embodiment of the present invention,showing reflectors around the perimeter of the output end of a taperedlight pipe;

FIG. 6 is a cross-sectional side view of a decreasingly tapered lightpipe angularly recycling light in accordance with an exemplaryembodiment of the present invention;

FIG. 7 is a cross-sectional side view of an illumination systemcomprising decreasingly tapered light pipe of FIG. 6 in accordance withan exemplary embodiment of the present invention having a tapered lightpipe;

FIG. 8 is a cross-sectional side view of an illumination systemcomprising two tapered light pipes coupled to each other in accordancewith an exemplary embodiment of the present invention;

FIGS. 9 a-b are cross-sectional side views of an illumination systemcomprising two LEDs mounted on a substrate with a reflective coatingdisposed on the substrate between the LED's and respectively coupled toa straight or tapered light pipe in accordance with an exemplaryembodiment of the present invention;

FIGS. 10 a-b are cross-sectional side views of an illumination systemcomprising two LEDs mounted on a substrate and respectively coupled to astraight or tapered light pipe with a reflective coating disposed on theinput end of the light pipe between the LED's in accordance with anexemplary embodiment of the present invention;

FIG. 11 a is a cross-sectional side view of an illumination systemcomprising two tapered light pipes, each tapered light pipe coupled atthe input end to a LED and at the output end to a same straight lightpipe having a reflector covering a portion of its output end tospatially recycle light in accordance with an exemplary embodiment ofthe present invention;

FIG. 11 b FIG. 11 a is a cross-sectional side view of an illuminationsystem comprising two tapered light pipes, each tapered light pipecoupled at the input end to a LED and at the output end to a samedecreasingly tapered light pipe to angularly recycle light in accordancewith an exemplary embodiment of the present invention;

FIG. 12 shows a cross-sectional side view of the illumination system ofFIG. 11 a additionally comprising a reflective polarizer covering theoutput end of the straight light pipe in accordance with an exemplaryembodiment of the present invention;

FIGS. 13 a-d are cross-sectional side views of an illumination systemcomprising color beam combiners, coupled to straight or tapered lightpipe, for combining the output of three LED chips in accordance with anexemplary embodiment of the present invention;

FIGS. 14 a-b are cross-sectional views of an illumination systemcomprising a mounting frame for mounting a glass plate and a straight ortapered light pipe coupled to an LED on a substrate in accordance withan exemplary embodiment of the present invention;

FIGS. 15 a-b are the illumination systems of FIGS. 14 a-b comprising twoLED chips;

FIG. 16 is a cross-sectional side view of an illumination systemcomprising a solid optical component having a lens surface for couplingsmall angle rays of light and two concave reflective surfaces forretro-reflecting large angle rays of light to angularly recycle light inaccordance with an exemplary embodiment of the present invention;

FIG. 17 is a cross-sectional side view of an illumination systemcomprising a lens for coupling small angle rays of light and concavereflectors for retro-reflecting large angle rays of light to angularlyrecycle light in accordance with an exemplary embodiment of the presentinvention;

FIG. 18 is a cross-sectional side view of an illumination system of FIG.16 or 17 for angularly recycling light using dual paraboloid reflectorsor reflective surfaces in accordance with an exemplary embodiment of thepresent invention;

FIG. 19 is a cross-sectional side view of a LED illumination systemincorporating the optical recycling device in accordance with anexemplary embodiment of the present invention;

FIG. 20 is a cross-sectional side view of a LED illumination systemhaving LED chip with integrated optics incorporating the opticalrecycling device in accordance with an exemplary embodiment of thepresent invention

FIG. 21 is a cross-sectional side view of a LED projection systemincorporating the optical recycling device in accordance with anexemplary embodiment of the present invention;

FIG. 22 is a cross-sectional side view of a fiber optics systemincorporating the optical recycling device in accordance with anexemplary embodiment of the present invention;

FIG. 23 is a cross-sectional side view of a LED projection system ofFIG. 21 or fiber optics system of FIG. 22 having LED chip withintegrated optics;

FIG. 24 illustrates calculated brightness enhancement curves for variousLED reflectivity in accordance with an exemplary embodiment of thepresent invention;

FIG. 25 illustrates experimental brightness enhancement curves forvarious LED reflectivity in accordance with an exemplary embodiment ofthe present invention; and

FIG. 26 illustrates calculated brightness enhancement curves with LED inclose proximity to the light pipe in accordance with an exemplaryembodiment of the present invention.

DETAILED DESCRIPTION

With reference to the figures, exemplary embodiments of the inventionare now described. These embodiments illustrate principles of theinvention and should not be construed as limiting the scope of theinvention.

In accordance with exemplary embodiments of the present invention, asshown in FIGS. 3-5, 7-18, the illumination system 1000 for recyclinglight to increase the brightness of the light source comprises a lightsource 100 and an optical recycling device 200. As shown in FIG. 1, thelight source 100 is mounted on a substrate 140. The substrate 140 ispreferably though not limited to a heatsink 140 for absorbing anddissipating heat emitted from light source 100. Light source 100 ispreferably a light emitting diode (“LED”). The LED or light source 100can be mounted to the substrate 140 as a bare chip, a chip with aprotective coating, or a chip with a lens or collimating lens mountedthereon. The chip size can be as small as less than 1 mm by 1 mm, or aslarge as technologically feasible. Commercial chips can be as large as 3to 5 mm in dimension. The dimension of such chips is increasing overtime as technology matures. The lens mounted on the LED chip 100 can bespherical in shape or tailored to any shape of the chip to achievemaximum coupling such as aspheric, or a combination of shaped lens fortransmission and shaped surfaces for reflection. Although the presentillumination system is described using an LED as the light source 100,the light source 100 can be any light source including but not limitedto arc lamps, halogen lamps, surface emitting devices (SEDs),fluorescent devices, microwave lamps, and other light sources asunderstood by those of skill in the art. In accordance with anembodiment of the present invention, as shown in FIGS. 9 a-13 d and 15a-b, the present system can comprise a plurality of light sources 100mounted on a single substrate 140. In accordance with an aspect of thepresent invention, each light source 100 can be mounted on a separatesubstrate 140 as shown in FIGS. 11 a-12.

In accordance with exemplary embodiment of the present invention, theoptical device 200 can be a spatial and/or angular recycling devicewhich is in optical communication with light source 100. As describedherein, the spatial or angular recycling device 200 generally comprisesa light pipe 300 which can be straight or tapered. As shown in FIG. 2,the output of the light source or LED 100 is coupled to the light pipe300 to provide a uniform intensity profile of the light at the outputend 320 of the light pipe 300. The light in the light pipe 300 beingguided to the output end 320 through total internal reflection. Theoutput of the LED 100 is captured by the light pipe 300 and transmittedto the output end 320 of the light pipe 300. The light pipe 300 can berectangular, hexagonal or triangular in shape. Preferably, the shape ofthe light pipe 300 matches the shape of the light source or LED 100 forhigh coupling efficiency. In the ideal case, the output of the LED 100is totally captured by the light pipe 300. When the cross-sectionaldimensions of the light pipe 300 matches the LED 100, the outputbrightness at the output end 320 of the light pipe 300 will generally besame as the output brightness of the LED 100. However, in commercialapplication, one can expect some coupling loss between the LED 100 andthe light pipe 300 and transmission loss within the light pipe 300.

In accordance with exemplary embodiments of the present invention, asshown in FIGS. 3-5, 9 a, 10 a, 11 a, 12, 13 a, 14 a, and 15 a, thespatial optical recycling device 200 comprises a light pipe 300 and areflector, mirror, reflective medium or reflector system 400 coupled tothe output end 320 of the light pipe 300. The input end 310 of the lightpipe 300 is in optical communication with or coupled to the light source100 and the output end 320 is coupled to the reflective medium 400. Theoptical communication can be accomplished by placing the light pipe 300in proximity with the light source 100 such that the input end 310 ofthe light pipe 300 collects light emitted from the light source 100. Inthe alternative, the input end 310 of the light pipe 300 can be affixedor glued to the light source 100 using epoxy or any other such heatresistant, transparent connecting material. It is appreciated that thelight pipe 300 can be hollow or solid and can have any cross-sectionaldimensional shape including but not limited to rectangular, hexagonal,triangular, etc. Preferably, the shape of the light pipe 300 preferablymatches the shape of the light source or LED 100 for high couplingefficiency.

The light pipe 300 can be of uniform cross-sectional dimension or can betapered having either increasing or decreasing cross-sectional dimensionfrom the input end 310 to the output end 320. The optical recyclingdevice 200 comprising a light pipe 300 with an increasingcross-sectional dimension can reduce the output numerical aperture.Whereas, the optical recycling device 200 comprising a light pipe 300with a decreasing cross-sectional dimension can enhance the recycling oflight at large angles, thereby providing angular recycling of the light.

The light pipe 300 can be made of glass, quartz, plastic, fused silica,acrylic, and the like. The light pipe 300 can have bare surfaces orsurfaces coated with material of low refractive index for light guidingsimilar to standard optical fibers or the light pipe 300 can have any orall of its surfaces coated with a reflective coating such as aluminum.Although the recycling light pipe 300 described and shown herein is asolid light pipe, in practice and commercial application, the light pipe300 can be hollow with openings at the input and output ends 310, 320and mirrors forming the reflecting surfaces. Openings at the input andoutput ends 310, 320 can be coated with anti-reflective material toincrease the efficiency of the light pipe 300 in recycling the light.

The reflective medium 400 is mounted on the output end of the light pipe300 and covers a portion of the output end 320 of the light pipe 300.The reflective medium 400 can be an external reflector, mirror orreflective coated material. Alternatively, the reflective medium 400 canbe integrated with the light pipe 300, such as depositing the output end320 of the light pipe 300 with reflective coating. Since the reflectivemedium 400 covers the portion of the output end 320 of the light pipe300, a portion of the light from the light source 100 is reflected backinto the light pipe 300. The reflected light 110 is transmitted to thelight source 100 by the light pipe 300 and re-emitted or reflected backinto the light pipe 300 as an output from the light source 100, as shownin FIG. 3. Since the area of the output end 320 of the light pipe 300 isreduced by the reflector 400, any light reflected back into the lightpipe 300 by the reflector 400 will enhance or increase the brightness ofthe light being outputted from the light source 100 and exiting thelight pipe 300, thereby increasing the brightness of the illuminationsystem in accordance with an embodiment of the present invention.Although the overall output power will be smaller from the light pipe300, the brightness of the light output will be increased by therecycling of a portion of the light from the light source 100 by theoptical recycling device 200 of the present invention.

Typically, the LED chip or die 100 has a certain reflectivity defined bythe ratio of light reflectivity off the surface compared to the amountof light incidence onto the surface. The surface of the LED chip 100 isalso non-specula, which is defined by the scattering factor. Thetheoretical recycling efficiency of the spatial recycling device 200calculated by ray tracing for various LED reflectivity is shown in FIG.24. The brightness enhancement of the spatial recycling device 200 ofthe present invention is plotted against the number of LEDs 100, whichis inverse of the percentage (%) of opening at the output end 320 of thelight pipe 300. For example, the output of the spatial recycling device200 of the present invention is 1.9 times brighter for a LEDreflectivity of 60% for 20% opening at the output end 320 (correspondingto five LEDs) of the light pipe 300.

Experimental results plotted against the theoretical curves of FIG. 24are shown in FIG. 25 of the spatial recycling device 200 using an LEDmade by an undisclosed vendor. A mirror 400 was placed at the output end320 of the light pipe 300 such that the mirror can be adjusted toprovide various percent openings. Since the LED chip 100 was mounted onthe heat sink 140 with a transparent window, as a result, the couplingefficiency was not 100% between the LED 100 and the light pipe 300.Additionally, the reflectivity of the mirror 400 at the output end 320of the light pipe 300 was not 100%. Because of the reflectivity loss ofthe LED 100 and other experimental imperfections contributing to theloss, the observed reflective was less than the reflectivity of the LED.The physical model of the experimental spatial recycling device 200 wasobtained with an ASAP ray tracing program with R (reflectivity) and S(scattering) of the LED as curve fitting parameters. At the best fit,the reflectivity R was found to be 52% and the scattering S was found tobe 18 degrees. Also, ASAP ray tracing was performed with window removedsuch that the light pipe 300 is in close proximity to the LED die 100.FIG. 26 shows the calculated brightness enhancement with the LED die 100in direct contact with the light pipe 300 versus the number of LEDs 100,which is inverse of the percentage (%) of opening at the output end 320of the light pipe 300. For example, the brightness enhancement of 1.6times can be obtained for this LED die 100 using the spatial recyclingdevice 200 of the present for 20% opening at the output end 320(corresponding to five LEDs) of the light pipe 300.

In accordance with an exemplary embodiment of the present invention, asshown in FIG. 4, the optical recycling device 200 includes a polarizingbeam splitter (PBS) 220 or polarizer 210, preferably a reflectivepolarizer 210, to provide a polarized illumination system 1000. Thereflective polarizer 210 or PBS 220 can cover the entire output end 320of the light pipe 300 or only portion of the output end 320 not coveredby the reflector 400. Additionally, the reflective polarizer 210 or PBS220 can be placed or mounted on the output end 320 of the light pipe 300before or after the reflector 400. The reflective polarizer 210 or PBS220 reflects the light with undesirable or unwanted polarization backinto the light pipe 300, thereby enhancing the recycling effect of theoptical recycling device 200 of the present invention and increasing thebrightness of the output light.

In accordance with an exemplary embodiment of the present invention, asshown in FIG. 4, the optical recycling device 200 includes a wave plate230 to promote scrambling of the light polarization state to increasethe efficiency of the optical recycling device 200. The wave plate 230can be placed between the output end 320 of the light pipe 300 and thereflective polarizer 210.

Referring now to FIG. 5, in accordance with an exemplary embodiment ofthe present invention, the spatial and angular recycling device 200comprises an LED chip 100, a tapered light pipe 300 where the input end310 is narrower than the output end 320, and a mirror 400 around theperimeter of the output end 320 of the tapered light pipe 300. The LEDChip 100 is mounted on the heatsink 140. The narrower input end 310 ofthe tapered light pipe 300 is in optical communication with LED chip100. It is appreciated that an air gap between the LED chip 100 and theinput end 310 of the tapered light pipe 300 can be filled low indexepoxy. The utilization of the tapered light pipe 300 in this embodimentof the present invention increases both the efficiency and brightnesswithin a certain cone angle. When LEDs 100 are used as the light source,the brightness is typically the most important parameter because usuallyonly the light output within a small angle can be collected. Forexample, the collection angle in a commercially available rearprojection television (RPTV) is estimated to be about 38 degrees and thelight emitted by the LEDs 100 in such RPTV from 38 to 90 degrees will benot utilized and wasted. The recycling tapered light pipe 300 of thepresent invention collects light from the LED 100, selects theappropriate angle of light to be transmitted as output and recycles therest of the light back to the LED 100, thereby recycling thenon-utilized light outside the selected angle to effectively increasethe brightness of the LED 100. The mirror 400 placed around theperimeter of the output end 320 of the light pipe 300 reflects the lightoutside the selected angle to the LED 100, thereby recycling the unusedlight. The amount of light outputted by the LED 100 using the spatialrecycling device 200 of the present invention within the selected angleis larger than the amount of light the LED 100 emits by itself withinthe selected angle, thereby increasing the brightness of the LED 100within the useable range.

In accordance with an exemplary embodiment of the present invention, asshown in FIGS. 14 a-b, the recycling or recovery light pipe 300(straight or tapered) of the present invention can be integrated withthe packaging of the LED 100. The LED 100 and a mounting frame 600 aremounted on the heatsink or substrate 140. A glass plate or cover 650 ismounted on the mounting frame 600 and can be integrated with or attachedto the light pipe 300. The glass cover 650 also serves to protect theLED chip 100. The size of the mounting frame 600 can be adjusted tocontrol the gap 610 between the light pipe 300 and the LED chip 100.Preferably, the light pipe 300 is at close proximity to the LED chip 100for maximum coupling of light from the LED 100 into the light pipe 300and for light reflected back to the LED 100 through the light pipe 300by the mirror 400.

As shown in FIGS. 14 a-b, at the output end 320 of light pipe 300, aportion of the surface is covered with reflective surface (e.g.,reflective medium, coating or mirror 400) to promote recycling of lightwithin the light pipe 300. Preferably, the reflective medium 400 isaround the perimeter of the surface of the output end 320 of the lightpipe 300. Although not shown, other configurations can be used, such ascovering the part of the output surface with the reflective medium 400biased to one side or the other. As noted herein, the light pipe 300 canbe attached to the glass cover 650 to facilitate mounting of variousoptical components of the optical recycling device 200. The assemblyprocess for an integrated light pipe of the present invention is similarto the standard LED assembly except that the glass cover 650 is formedtogether with the light pipe 300. It is appreciated that the tight pipe300 can be tapered (decreasing or increasing), straight, solid or hollowdepending on the application. A hollow tight pipe can be assembled byattaching four mirrors to the cover glass 650 by epoxy, solder, or otherattachment means.

In accordance with an exemplary embodiment of the present invention, thestraight or tapered light pipe 300 can be integrated with the packagingof a multiple LED chips 100, such as two LED chips 100 in FIGS. 15 a-b.Multiple LEDs or LED chips 100 are mounted on the heatsink or substrate140 with a single mounting frame 600. As shown in FIGS. 15 a-b, at theinput end 310 of the light pipe 300, the surface corresponding to thespace between the LED chips 100 are coated with reflective coatingpromote recycling of the light within the light pipe 300.

It is appreciated that most LEDs have Lambertian emission pattern.Special LEDs made with photonic lattice has emission pattern that isenhanced at small angle such the brightness is higher. In either case,the brightness at small angle is higher than the brightness at higherangle. As a result, if higher brightness is desired, only small angleemission can be used, this wasting all the high angle emissions. Theresulting system is very inefficient. To overcome this shortcoming, anangular recycling system is used such that the high angle emission isreflected back into the LED and only low angle emission is beingtransmitted. FIG. 5 shows the schematic diagram of an angular recyclingsystem.

Referring to FIGS. 6-8, 9 b, 10 b, 11 b, 13 c-d, 14 b and 15 b, inaccordance with exemplary embodiments of the present invention, theoptical recycling device 200 comprises a hollow or solid tapered lightpipe 300. FIG. 6 shows an angular recycling device 200 comprising adecreasingly tapered light pipe 300 tapering from a larger area to asmall area (the input end 310 is larger than the output end 320). Thisdecreasingly tapered light pipe 300 can be used to filter out inputlight with large incidence angles. That is, input light with largeincidence angles are reflected and only input light with small incidenceangles are transmitted by the decreasingly tapered light pipe 300. Theinput light ray a0 entering the input end 310 of the decreasinglytapered light pipe 300 at an incidence angle of θa is reflected insidethe decreasingly tapered light pipe 300 multiple times and exits throughthe output end 320 of the decreasingly tapered light pipe 300 as outputray a1. It is appreciated that input light ray can exit the increasinglytapered light pipe 300 with a larger degree of incidence. The light rayb0 entering the input end 310 of the decreasingly tapered light pipe 300at a large incidence angle of θb is also reflected multiple times withinthe decreasingly tapered light pipe 300, but before reaching the outputend 320 of the decreasingly tapered light pipe 300, the angle of thelight ray b0 reaches beyond 90 degrees of incidence. The light ray b0starts to reflect back towards the input end 310 of the decreasinglytapered light pipe 300 and exits the input end 310 rather than theoutput end 320 of the decreasingly tapered light pipe 300 as light rayb1, as shown in FIG. 6. The decreasingly tapered light pipe 300 ineffect acts as an angle filter for the incident input light, in whichlight with small incidence angles are transmitted and light with largeincidence angles are rejected or reflected by the decreasingly taperedlight pipe 300.

In accordance with exemplary embodiments of the present invention, asshown in FIGS. 7-8, 9 b, 10 b, 11 b, 13 c-d, 14 b and 15 b, the angularrecycling device 200 comprises decreasingly tapered light pipe 300 and aplurality of LEDs 100, An LED 100 is placed in front of the input end310 of the decreasingly tapered light pipe 300 with the area of the LED100 being substantially the same as the area of the input end 310 of thedecreasingly tapered light pipe 300. The light with a high angle ofincidence or high angle light is reflected back into the LED 100 by thedecreasingly tapered light pipe 300 of the present invention. Thereflected light is recycled in the LED 100 and reflected back into thedecreasingly tapered light pipe 300 with a different angulardistribution than the original input light. That is, a portion of therecycled reflected light now has a small angle of incidence (or smallangle light) to be transmitted by the decreasingly tapered light pipe300 and coupled to the output of the decreasingly tapered light pipe300. The small angle light exits the output end 320 of the decreasinglytapered light pipe 300 as an output. Since the LED surface hasscattering, part of the reflected light at higher angle is scattered tolower angled and coupled out of the angular recycling device 200,thereby increasing the brightness of the illumination system 1000. Inaccordance with an exemplary embodiment of the present invention, asshown in FIG. 8, the output end 320 of the decreasingly tapered lightpipe 300 can be coupled to the input end 310 of another tapered lightpipe 300 (preferably, increasingly tapered light pipe), thereby reducingthe high angle light from the LED but increasing the light output area.

In accordance with exemplary embodiments of the present invention, theillumination system 1000 comprises a plurality of LEDs 100 coupled to asingle output light pipe 300. Turning now to FIGS. 11 a-b and 12, twoLEDs 100 are coupled to a single output light pipe 300 (straight lightpipe as in FIG. 11 a or tapered light pipe as in FIG. 11 b) using twotapered input light pipes 350, preferable increasingly tapered lightpipes 350, in accordance with an exemplary embodiment of the presentinvention. The input ends of the tapered input light pipes 350 arerespectively coupled to two LEDs 100 and the output ends of the taperedinput light pipes 350 are coupled to the output light pipe 300. As notedherein, the output end 320 of the output light pipe 300 is partiallycoated with reflective coating or medium to promote recycling within theoptical recycling device 200, thereby increasing the brightness of theillumination system 1000. The dimensions of the output ends of thetapered input light pipes 350 are preferably matched to the dimensionsof the input end of the output light pipe 300, such that there areminimal gaps between the output ends of input light pipes 350 to achievehigh coupling of light.

In accordance with exemplary embodiments of the present invention, asshown in FIGS. 9 a-b, 10 a-b, 11 a-b and 12, the illumination system1000 comprises a plurality of LED chips or LEDs 100, preferably closelypacked, in a single dimension (i.e., a row of LEDs) or in atwo-dimensional array. Preferably, as shown in FIGS. 11 a-b and 12, theLEDs/LED chips 100 and the input light pipes 350 are densely or closelypacked. The shapes of the LEDs 100 and the input light pipes 350 can becircular, triangular, hexagonal, octagonal and the like. Although thedimensions of the LEDs 100 and input light pipes 350 can be uniform, butit can vary depending on the application of the illumination system.That is, the optical recycling device 200 can comprises a plurality ofLEDs 100 having varying shapes and sizes and a plurality of input lightpipes 350 having varying shapes and sizes. In accordance with anexemplary embodiment, the LED 100 and the input light pipe 350 that theLED 100 is coupled to (i.e., LED-light pipe pair) have the substantiallysimilar shape. For example, a triangular shaped input light pipe 350 iscoupled to a triangular shaped LED 100. This advantageously permits theillumination system 1000 of the present invention to be designed toprovide a particular output power by combining existing and readilyavailable LEDs 100 of varying output power and size. Moreover, theutilization of multiple LEDs 100 additionally provides averaging effectsfor output power and wavelength. Typically in LED production, the outputpower and wavelength of the LEDs/LED chips are not well controlled.Current LED production requires the “binning” of LED chips with severalwavelengths and several power ranges. When several LEDs are combinedinto a single source of output in accordance with various embodiments ofthe present invention, the average variation of the illumination system1000 (or a light source) as a whole is smaller in both output power andwavelength. It is appreciated that when sufficient LEDs are used as asingle source of light output as in various embodiments of the presentinvention, the binning may not be required, thereby improving the yieldof LEDs/LED chips and saving manufacturing cost.

Typically two or more colors are used in a color projection system. Inaccordance with an exemplary embodiment of the present invention, theillumination system 1000 comprises various colored LEDs or LED chips100, which can be combined and mixed, for example, using techniquesdisclosed in co-pending application Ser. No. 11/351,013entitled EtendueEfficient Combination of Multiple Light Sources, owned by the commonassignee of this application, which is incorporated herein by referencein its entirety. That is, for example, the present invention can beutilized to provide 3-color (red, green and blue) projection systems, or4-color and 5-color projections systems, which are starting to gain somemomentum.

In accordance with exemplary embodiments of the present invention, asshown in FIGS. 9 a-b and 10 a-b, the optical recycling device 200comprises multiple LED chips 100 coupled to the input end 310 of thelight pipe 300. As noted herein, the LED chips 100 are densely packed byminimizing the spacing between the LED chips 100. Although the spacesbetween the LED chips 100 can be made reflective, partially reflectiveor non-reflective, the spaces are preferably reflective to promoterecycling of the light, thereby increasing the efficiency of the opticalrecycling device 200. In accordance with an exemplary embodiment of thepresent invention, as shown in FIGS. 9 a-b, the surface of the substrate140 between the LED chips 100 (i.e., spaces 130) are made reflectiveusing reflectors, mirrors, reflective coating and the like.Alternatively, as shown in FIGS. 10 a-b, the input end 310 of the lightpipe 300 corresponding to the spaces 130 between the LED chips 100 canbe made reflective using reflectors, mirrors, reflective coating and thelike. Although only increasingly tapered light pipe 300 is shown inFIGS. 9 b and 10 b, either increasingly (a small input end to a largeoutput end) or decreasingly (a large input end to a small output end)tapered light pipe 300 can be used. The increasingly tapered light pipe300 can be used to reduce the output numerical aperture and thedecreasingly tapered light pipe 300 can be used to enhance recyclinglight at large incidence angles.

In accordance with an exemplary embodiment of the present invention, asshown in FIGS. 13 a and 13 b, the illumination system 1000 comprises alight pipe 300 (which can be either a straight or tapered light pipe)and a color beam combiner 700 for combining output from various coloredLEDs 100 (e.g., each LED 100 emitting light having differentwavelengths) into a single output 250. As shown in FIG. 13 a, the colorbeam combiner 700 comprises cube prisms P1, P2, P3 (preferably,polarization beam splitters) and cubes G1, G2 for combining output fromvarious colored LEDs 100, such as red, blue and green LEDs 100. The cubeprism P3 is coupled to the input end 310 of the light pipe 300. The redLED (R-LED) 100 emits red light which is reflected by the cube prism P1and into the cube G1. The cube prism P2 transmits the red light receivedfrom the cube G1 and reflects the green light emitted by the green LED(G-LED) 100. The cube prism P2 transmits both the reflected green lightand transmitted red light into cube G2. The cube prism P3 transmits boththe green and red light received from the cube G2, and reflects the bluelight emitted by the blue LED (B-LED) 100 into the light pipe 300.Preferably, all sides of the cube prisms 710, cubes 720, and the lightpipe 300 are polished to efficiently guide through the various opticalcomponents of the illumination system 1000. As noted herein, the outputend 320 of the light pipe 300 has a reflective coating, reflector ormirror 400 covering a portion of the output end 320 to promoterecycling, thereby increasing the brightness of the illumination system1000.

Alternatively, the color beam combiner 700, such as triangular prisms730, and light pipe 300 are integrated into a single piece. As shown inFIG. 13 b, the illumination system 1000 comprises R-LED 100, G-LED 100,B-LED 100, waveguide sections W1-W5 and an output section 300 (which canbe either tapered or straight). Preferably, the waveguide sections W1,W3 and W5 are triangular prisms. The red LED (R-LED) 100 emits red lightwhich is reflected by the waveguide section WI and into the waveguidesection W2. The waveguide section W3 transmits the red light receivedfrom the waveguide section W2 and reflects the green light emitted bythe green LED (G-LED) 100. The waveguide section W3 transmits both thereflected green light and transmitted red light into waveguide sectionW4. The waveguide section W5 transmits both the green and red lightreceived from the waveguide section W4, and reflects the blue lightemitted by the blue LED (B-LED) 100 into the output section 300. Anexample of color beam combiner is disclosed in co-pending applicationSer. No. 11/351,013, which is incorporated herein by reference in itsentirety. Preferably, all sides of the waveguide sections W1-W5 and theoutput section 300 are polished to efficiently guide through the variousoptical components of the illumination system 1000. As noted herein, theoutput end 320 of the output section 300 has a reflective coating,reflector or mirror 400 covering a portion of the output end 320 topromote recycling, thereby increasing the brightness of the illuminationsystem 1000.

In accordance with an exemplary embodiment of the present invention, theillumination system 1000 comprises an angular recycling device 200. Asshown in FIG. 16, the angular recycling device 200 comprises a LED 100mounted on a heatsink 140 and a solid optical component made of plasticor glass 800 having reflective concave surfaces 820, 830 and lenssurface 810. Preferably, the reflective concave surfaces 820, 830surrounds the lens surface 810. The shape of the reflective concavesurfaces 820, 830 can be spherical, parabolic or elliptical and can bemade reflective by reflective coating. The reflective surfaces 820, 830act as retro-reflectors to reflect high angle rays back into the LED 100for recycling. The small angle rays (core angle shown in FIG. 16 as theangle between dotted lines 1061) of light from the LED 100 are coupledby the lens surface 810 and outputted from the angular recycling device200 as output 250.

Alternatively, as shown in FIG. 17, the angular recycling device 200comprises a LED 100 mounted on a heat sink 140, reflectors 840, 850 andlens 860. The high angle rays from the LED 100 are reflected by thereflectors 840, 850 back into the LED for recycling and the small anglerays from the LED 100 are coupled by the lens 860 and outputted from theangular recycling device 200 as output 250.

In accordance with an exemplary embodiment of the present invention, asshown in FIG, 18, the angular device 200 of FIGS. 16, 17 comprises dualparaboloid reflectors 840, 850 or the reflective surfaces 820, 830 actas dual paraboloid reflectors to reflect the high angle rays twicebefore being focused back onto the LED 100. That is, the light reflectedfrom the reflective surface 820 or reflector 840 is collimated andreceived by the reflective surface 830 or reflector 850, respectively.The collimated light is then refocused by the reflective surface 830 orreflector 850 and focused onto the LED 100 for recycling. Additionally,it is appreciated that the radius of curvature of reflective surfaces820, 830 and reflectors 840, 850 can be smaller than the radius ofcurvature of the lens surface 810 or lens 860 so that the reflectivesurfaces 820, 830 or reflectors 840, 850 can be closer to the LED thanthe lens surface 810 or lens 860.

In accordance with exemplary embodiment of the present invention, theoptical recycling device 200 of the present invention can beincorporated into a traditional LED illumination system to increase thebrightness of the LED source using spatial and/or angular recycling oflight. Typically in a traditional LED illumination system, the lightfrom the LED chips 100 is coupled to the application 900 (e.g.,projection display screen) through an external optical system 801. Asshown in FIG. 19, the spatial and/or angular optical recycling device200 of the present invention is inserted between the LED chips 100 andthe external optical system 801 to increase the brightness of the lightat the application 900.

Turning now to FIG. 20, the spatial and/or angular recycling device 200of the present invention can be incorporated into a traditional LEDillumination system having LED chip 100 with integrated optics 150, suchas a molded lens on the LED package, for extracting light from the LEDchip 100. Here, the spatial and/or angular recycling device 200 of thepresent invention is inserted between the integrated optics 150 and theexternal optical system 801 to increase the brightness of the light atthe application 900.

In accordance with exemplary embodiment of the present invention, theoptical recycling device 200 of the present invention can beincorporated into a traditional LED projection system to increase thebrightness of the LED source and/or amount of light coupled into theprojection system 950 using spatial and/or angular recycling of light.Typically in a traditional LED projection system, the light from the LEDchips 100 is coupled to the projection system 950 using a lens or lenssystem 810. As shown in FIG. 21, the spatial and/or angular opticalrecycling device 200 of the present invention is inserted between theLED chips 100 and the lens 810 to increase the brightness of the lightand/or amount of light coupled into the projection system 950.

In accordance with an embodiment of the present invention, as shown inFIG. 22, the spatial and/or angular recycling device 200 of the presentinvention can be incorporated into a fiber optics system to increase thebrightness of the LED source and total light coupled to a fiber optics920. Here, the spatial and/or angular recycling device 200 of thepresent invention is inserted between the LED chips 100 and the lens 810to increase the brightness of the light and/or amount of light coupledinto the fiber optics 920.

Turning now to FIG. 23, the spatial and/or angular recycling device 200of the present invention can be incorporated into the LED projectionsystem of FIG. 21 or the fiber optics system of FIG. 22 in which the LEDchip 100 comprises an integrated optics 850 for extracting light fromthe LED chip 100. Here, the spatial and/or angular recycling device 200of the present invention is inserted between the integrated optics 850and the lens 810 to increase the brightness of the light and/or amountof light coupled into the projection system 950 or the fiber optics 920.

The invention, having been described, it will be apparent to thoseskilled in the art that the same may be varied in many ways withoutdeparting from the spirit and scope of the invention, Any and all suchmodifications are intended to be included within the scope of thefollowing claims.

1. An illumination system for increasing the brightness of a lightsource, comprising: a light source for emitting a plurality of rays oflight in a direction generally centered about an axis, wherein a firstplurality of said rays are emitted within a low angle range relative tosaid axis, and wherein a second plurality of said rays are emittedwithin a higher angle range up to 90 degrees relative to said axis; andan optical recycling device coupled to said light source for receivingsubstantially all of said plurality of rays of light from said lightsource; wherein said recycling device has an annular opening, centeredon said axis, for transmitting only said first plurality of said rays,and an annular, concave reflective portion having a reflective surfacesurrounding said axis, said concave portion extending axially from saidopening towards said light source a sufficient distance to capturesubstantially all of said second plurality of rays and redirect saidsecond plurality of rays of light directly back to said light sourcewhich re-emits said portion of said plurality of rays of light to saidoptical recycling device, thereby increasing the brightness of saidlight source's output.
 2. The illumination system of claim 1, whereinsaid optical recycling device comprises a solid optical component havinga lens surface disposed in said annular opening said first plurality ofrays of light.
 3. The illumination system of claim 2, wherein said solidoptical component has at least a generally hemispherical shape such thatsaid reflective surface has a spherical or elliptical shape, and whereina flat surface of said solid optical component is disposed to receivelight emitted by said light source.
 4. The illumination system of claim3, wherein the light source is an LED having a generally flat,light-emitting surface, and said flat surface is disposed against saidlight-emitting surface such that said recycling device capturessubstantially all light emitted by said LED.
 5. The illumination systemof claim 1, further comprising a lens disposed in said annular openingsuch that emitted light passes through, and is focused by, said lens. 6.A method for increasing the brightness of a light source, comprising thesteps of: providing a light source which emits light in a directiongenerally centered about a first axis, wherein a first plurality of saidrays are emitted within a low angle range relative to said axis, andwherein a second plurality of said rays are emitted within a higherangle range up to 90 degrees relative to said axis; providing arecycling device, which has an annular opening and an annular, concavereflective portion, having a reflective surface. centered about arecycling axis; coupling said recycling device to said light source suchthat said first axis and recycling axis are coplanar, such that saidfirst plurality of said rays extends through said annular opening andsuch that said annular, concave reflective portion surrounds said firstaxis, said concave portion extending axially from said opening towardssaid light source a sufficient distance to capture substantially all ofsaid second plurality of rays; and; recycling a portion of saidplurality of rays of light back to said light source; and re-emittingsaid portion of said plurality of rays of light to said opticalrecycling device by said light source, thereby increasing the brightnessof said light source's output.
 7. The method of claim 6, wherein saidoptical recycling device is a spatial recycling device; and wherein thestep of recycling comprises the step of spatially recycling said portionof said plurality of rays of light by reflecting said portion of saidplurality of rays of light back to said light source.
 8. The method ofclaim 7, wherein the step of spatially recycling comprises the step ofreflecting said second plurality of rays of light back to said lightsource, thereby providing both spatial and angular recycling of light.9. The method of claim 7, wherein said light source is a plurality ofcolored LED chips; and further comprising the steps of receiving saidplurality of rays of light having different wavelength from saidplurality of colored LED chips and combining said plurality of rays oflight from said plurality of colored LED chips.
 10. An illuminationsystem for increasing the brightness of a light source, comprising: alight source for emitting a plurality of rays of light generally aboutan axis, wherein a first plurality of said rays are emitted within a lowangle range relative to said axis, and wherein a second plurality ofsaid rays are emitted within a higher angle range up to 90 degreesrelative to said axis; and an optical recycling device coupled to saidlight source for receiving substantially all of said plurality of raysof light from said light source; wherein said recycling device has anannular opening, centered on said axis, for transmitting only said firstplurality of said rays, and an annular, concave reflective portionhaving a reflective surface surrounding said axis, said concave portionextending axially from said opening towards said light source asufficient distance to capture substantially all of said secondplurality of rays and redirect said second plurality of rays of lightback to said light source which re-emits said portion of said pluralityof rays of light to said optical recycling device, thereby increasingthe brightness of said light source's output, wherein said concaveportion forms a dual paraboloid reflector to reflect said secondplurality of rays of light once toward an opposing surface of said dualparaboloid reflector, from where it is focused back onto said lightsource.